This invention relates generally to improvements in surge arresters and more particularly to surge arresters having an arc discharge gap of the type used for protecting telephone lines and other communication lines from over-voltage conditions.
Surge arresters known in the prior art generally comprise a housing that contains a pair of spaced carbon electrodes that define an arc or discharge gap therebetween for grounding excessive line voltages so as to protect both equipment on the line and the line itself. With repeated overvoltage conditions and discharges, carbon particles tend to erupt from the electrode surfaces. These particles often become lodged between the electrodes causing a "noisy" line or even a complete grounding of the line, resulting in failure of the surge arrester after a relatively small number of discharges.
In the design of surge arresters of the foregoing type, a compromise is required between an adequate surge lift (i.e., number of firings) and acceptably low breakdown voltage. Thus, the arc gap can be widened to reduce the possibility of failure due to the presence of lodged carbon particles resulting from eruption during firing. This will, of course, increase the surge life of the arrester. However, widening the arc gap tends to increase the breakdown voltage of the unit beyond acceptable standards.
Also known in the prior art is the idea of providing a plurality of rectangular plateaus and grooves in the faces of the carbon electrodes to provide some release space for the erupted particles to be blown away from the arc gap. This type of a structure is generally known from U.S. Pat. Nos. 571,699 to DeKhotinsky dated Nov. 17, 1896 and Yearance et al. 3,703,665 dated Nov. 21, 1972. However, this arrangement produces multiple discharge surfaces, whereas, for consistent performance of a surge arrester, it is now thought that there should be only a single continuous surface for arc discharge. Further, the plateau in groove or "peak and valley" arrangement is generally maintained on only one of the two electrode faces, resulting in polarity sensitivity of the arrester. That is, the performance of the arrester with the electrodes held at one polarity is not consistent with the performance at the opposite polarity. Further, the peak and valley arrangement of the one electrode face generally lowers the effective surface of the electrode forming the arc gap. Thus, the wearing away of the peak portions of the electrode face, due to particle eruption therefrom during discharge, often results in a widening of the arc gap, thereby increasing the breakdown voltage of the arrester beyond acceptable standards. Further, electrodes of the plateau and groove type are relatively difficult and expensive to manufacture accurately.